S- and Cl-functionalized Nb2C MXenes as novel anode materials for sodium-ion batteries: a first-principles study

Abstract

MXenes are attracting much attention as electrode materials due to their excellent energy storage and electrochemical properties. More interestingly, the energy storage capacities of MXenes have been found to strongly depend on the surface terminal groups. Here, first-principles calculations were performed to investigate the geometric stability, electrochemical properties and Na storage capability of Nb₂CT₂ (T = O, S, Se, Cl or Br) systems based on density functional theory. The results reveal that the superior properties such as good electronic conductivity, fast charge–discharge rates, low open circuit voltage and high theoretical Na storage capacity make Nb₂CS₂ and Nb₂CCl₂ applicable for novel anode materials in sodium-ion batteries (SIBs) compared with the other Nb₂CT₂ (T = O, Se or Br) MXenes. Moreover, S- and Cl-functionalization can yield expanded interlayer spacing, improving the Na ion accessibility in Nb₂CT₂. These findings provide guidance for the design of MXene-based anode materials in SIBs.